Cumali Sabah

A Tunable Metamaterial Resonator Using Varactor Diodes to Facilitate the Design of Reconfigurable Microwave Circuits

In this brief, we designed, constructed, and analyzed a frequency-tunable metamaterial resonator. The proposed design consists of an S-shaped resonator, a ground frame, and a feeding transmission line. First, the structure is designed as a nontunable resonator and then tunability is achieved by employing varactor diodes. In order to verify and demonstrate its tunable metamaterial properties, reflection and transmission parameters, group delay, electric and magnetic field distributions, and permittivity and permeability at each tuned frequency were analyzed. Simulation and measured results agree well and show that a high transmission and reflection peak occurs at each resonance frequency that may be tuned with the applied control voltage. Therefore, the proposed tunable metamaterial resonator may be used to realize reconfigurable microwave circuits such as reflection/transmission filters, antennas, and sensors, and for achieving flexibility in many other microwave circuits.

Biosensor applications of chiral metamaterials for marrowbone temperature sensing

In this paper, we have designed, simulated, and analyzed a microwave biosensor based on chiral metamaterials (MTMs) to detect pig biological tissues which are widely used as a trial for medical explorations and researches. There are various types of biosensor structures based on MTMs in the literature. However, only a limited number of study is conducted on biosensors based on chiral MTMs; therefore, our study is one of the pioneer works for this type of research. The proposed diamond-shaped resonator-based structures are numerically investigated and analyzed in detail in the microwave frequency regime. The results are in good agreement which lead us to conclude that our structure can be easily used as an effective instrument for biosensing applications in medical technologies.

Multi-band polarization independent cylindrical metamaterial absorber and sensor application

A multi-band perfect metamaterial absorber (MA) based on a cylindrical waveguide with polarization independency is numerically presented and investigated in detail. The proposed absorber has a very simple configuration, and it operates at flexible frequency ranges within the microwave frequency regime by simply tuning the dimensions of the structure. The maximum absorption values are obtained as 99.9%, 97.5%, 85.8%, 68.2% and 40.2% at the frequencies of 1.34 GHz, 2.15 GHz, 3.2 GHz, 4.31 GHz and 5.41 GHz, respectively. The numerical studies verify that the proposed model can provide multi-band perfect absorptions at wide polarization and incident angles due to its rotational symmetry feature. We have also realized sensor and parametric study applications in order to show additional features of the suggested model. The suggested MA enables myriad potential applications in medical technologies, sensors and in defense industry etc.

Design and characterization of a resonator-based metamaterial and its sensor application using microstrip technology

Abstract. Design of a metamaterial based on an S-shaped resonator surrounded by a ground frame and excited by using a feeding transmission line on microstrip technology is presented. Since the resonator, ground frame, and its excitation mechanism are all realized on a microstrip, its characterization can be carried out using common laboratory equipment without needing any waveguide components or plane-wave-illumination techniques. The structure presented here may be realized on any microstrip and does not require special materials. The resonator and ground frame are both on the same side of the microstrip, thus the proposed topology may also be populated with active and passive microwave components, and hybrid active, passive, or reconfigurable microwave circuits may be realized. In metamaterial designs that require plane wave illumination, usually many numbers of periodic unit cells are needed; however, in our design, only one cell is capable of achieving metamaterial properties. The constitutive parameters of the metamaterial are retrieved and compared to demonstrate the agreement between simulations and measurements. The proposed topology is also demonstrated in a sensor application, where simulated and measured results agree well. Thus, it can be realized using standard microwave technology and used for numerous applications where metamaterial properties are needed.

Realization of polarization-angle-independent fishnet-based waveguide metamaterial comprised of octagon shaped resonators with sensor and absorber applications

A new fishnet-based waveguide metamaterial structure for the microwave region is introduced and investigated both numerically and experimentally. The proposed model is designed and fabricated on both sides of the substrate and exhibits strong metamaterial behavior (such as negative material parameters: i.e. negative permittivity, negative permeability, and negative index of refraction) at the resonance. Only one single slab is used in the simulation and experiment which provides a reduction in the number of the required samples with respect to its free-space and/or waveguide counterparts. This means that a small-sized metamaterial structure is simulated, measured, and characterized by placing the sample in the waveguide. The effective medium theory is employed for the characterization of the structure and the left-handed region is identified. The measured results are in good agreement with the simulated ones which show that the proposed structure operates well in terms of metamaterial behavior and can be used in waveguide miniaturization and waveguide-based applications such as antennas, filters, sensors, absorbers, imaging systems, and so on. To validate this claim, sensor and absorber applications are selected and the simulation results show that the proposed sensor and absorbers devices operate well under the defined conditions.

Electromagnetic energy harvesting and density sensor application based on perfect metamaterial absorber

The proposed study presents an electromagnetic (EM) energy harvesting and density sensor application based on a perfect metamaterial absorber (MA) in microwave frequency regime. In order to verify the absorption behavior of the structure, its absorption behavior is experimentally tested along with the energy harvesting and sensing abilities. The absorption value is experimentally found 0.9 at the resonance frequency of 4.75 GHz. In order to harvest the EM energy, chips resistors are used. In addition, the suggested model is analyzed for its dependency on polarization angles. The results show that the perfect MA can be easily and efficiently used for EM energy harvesting applications. Moreover, as an additional feature of the model, we also realized a density sensor application. It can be seen that this structure can be used as a multi-functional device and configured for many other sensing applications.

Graphene-based wideband metamaterial absorber for solar cells application

Abstract. A wideband metamaterial (MTM) absorber based on a concentric ring resonator is discussed at visible frequencies. The proposed structure offers a wideband absorption response, where absorption of >70% is gained for the frequency ranging from 537.91 to 635.73 THz. The analysis is conducted on the components of the proposed structure to understand the origin of wideband absorption. Furthermore, a graphene monolayer sheet is integrated to the proposed MTM absorber to optimize its absorptivity, where the studies show enhancement of the absorptivity of the proposed structure up to 26% from its initial absorptivity. MTM absorbers of this kind have potential applications in solar cells.

New generation chiral metamaterials with small and flat chirality over a certain frequency band based on circular split ring resonators for microwave filter applications

There are many studies in literature on chiral metamaterials (MTMs) to obtain large chiralities with dynamic optical activities. With this regard, this new generation planar chiral MTM study focuses on a small, non-dispersive (constant/flat) chirality admittance over an indicated frequency band which has not been investigated so far in literature. This new generation planar chiral MTM provides a small and a constant/fixed chirality which is mostly ignored by the scientists. This study numerically and experimentally investigates and examines these new generation MTMs based on circular split ring resonators (SRRs) with an increased capacitance in details. Obtained results show that the suggested structure can provide a small and constant/flat chirality admittance over a certain frequency band and hence it can be used to design myriad novel electromagnetic (EM) devices such as transmission and antireflection filters, polarization rotators for any desired frequency regions.

New generation chiral metamaterials based on omega resonators with small and smooth chirality over a certain frequency band

In this paper, we have designed, simulated and analyzed a new generation chiral metamaterials (MTMs) with two geometries. There are various types of chiral MTM structures in the literature and almost all of them are indented to be designed for high level of chirality. In fact, small chirality and its application areas were mostly ignored by researchers. In this sense, our study is one of the pioneer works for this type of research. Each structure based on omega resonators (ORs) with small chirality value is investigated both numerically and experimentally. The results are in very good agreement which will lead us to conclude that our structures can be easily used as devices for controlling polarization, EM wave transmission filtering, antireflection and so on for a wide range of the EM spectrum.

Polarization angle independent metamaterial absorber based on circle-shaped resonators with interference theory

We theoretically and numerically designed a perfect metamaterial absorber at microwave frequencies. The proposed design has a very simple geometry, wide band properties and provides perfect absorption for all polarization angles which is one of the most desired properties for an absorber structure to be used in the applications where the source polarization is unknown. In order to explain the absorption mechanism both numerical and theoretical analyses are carried out. Designed structure offers a perfect absorption at around 9.8 GHz. The resonance frequency does not change depending on the source wave polarization. In addition, it can be easily reconfigured for THz and infrared regimes for different applications such as sensors, defense systems and stealth technologies.